Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor. The rotor typically includes a rotatable hub having one or more rotor blades attached thereto. A pitch bearing is typically configured operably between the hub and a blade root of the rotor blade to allow for rotation about a pitch axis. The rotor blades capture kinetic energy of wind using known aerodynamic principles. The rotor blades transform the kinetic energy in the form of mechanical energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
A plurality of wind turbines are commonly used in conjunction with one another to generate electricity and are commonly referred to as a “wind farm.” Wind turbines on a wind farm typically include their own meteorological monitors that perform, for example, temperature, wind speed, wind direction, barometric pressure, and/or air density measurements. In addition, a separate meteorological mast or tower (“met mast”) having higher quality meteorological instruments that can provide more accurate measurements at one point in the farm is commonly provided.
Traditionally, wind farms are controlled in a decentralized fashion to generate power such that each turbine is operated to maximize local energy output while also minimizing the impact of local fatigue and extreme loads. To this end, each turbine includes a control module, which typically attempts to maximize power output of the turbine in the face of varying wind and grid conditions, while satisfying constraints like sub-system ratings and component loads.
It is well known that large coherent structures in the wind cause extreme loads in wind turbines and determine the extreme design load envelope. The requirements for reacting to such coherent structures, which govern extreme loads acting on the wind turbine, are different than that for reacting to the normal turbulent wind, which govern fatigue loads. For example, when coherence is high, it is beneficial to have less smoothing in the wind estimation to preserve and respond to large and sharp wind gusts in full measure so as to reduce the extreme loads. On the other hand, during low wind coherence, less smoothing causes unnecessary pitch activity and fatigue, as the wind estimation responds to noise. Thus, to handle both extreme and fatigue loads, wind turbine controllers need to be able to detect large coherent structures in oncoming wind, as well as the ability to change the response strategy accordingly.
Coherence can be expressed at various time scales and can have different impact on turbine loading which may not be monotonic with the time scale of the transients. More specifically, coherence is usually high for slow wind transients, but does not pose a danger to turbine loads as they are easily rejected by the controller. For wind transients at medium timescales, coherence decreases but could pose increased risk to the turbine loading due to resonance with natural frequencies and the controller tuning. As very fast timescales, coherence would typically die down to not pose loading risk. Thus, understanding how the wind transients at various time-scales and coherence levels affect turbine component loading is essential in designing a metric of damaging or loads-relevant wind coherence.
Some conventional methods for estimating coherence for wind characterization utilize Fourier transforms to compute coherence spectra. Such methods, however, involve complex calculations at multiple discrete frequencies, averaging over large time intervals, and can be time-consuming to complete. Further, such methods are agnostic to the nature of wind transients that can worsen turbine loads. Therefore, such methods are typically incapable of providing quick detection of large coherent structures and subsequent control action thereof.
Accordingly, an improved system and method for estimating wind coherence and controlling wind turbines based on said coherence to prevent damage would be welcomed in the technology.